1. Field of the Invention
The present invention generally relates to optical pickup devices and, more particularly, is directed to an optical pickup device which drives and displaces in the focusing and tracking directions or in either of these focusing and tracking directions an objective lens which converges a laser beam emitted from a laser light source on a signal recording surface of an optical disc.
2. Description of the Prior Art
An optical pickup device is known as a device for reading an information signal recorded on an optical disc or recording a predetermined information signal on an optical disc by irradiating a laser beam on a signal recording surface of the optical disc which is revolved by a disc drive device. This known optical pickup device is provided with an objective lens drive device. The objective lens drive device drives and displaces in the focusing direction and in the tracking direction or in any one of these focusing and tracking directions an objective lens, which converges a laser beam emitted from a semiconductor laser provided as a laser light source on the signal recording surface of an optical disc, by a magnetic drive force so that the laser beam is focused on the signal recording surface of the optical disc thereby accurately scanning recorded tracks formed on the optical disc.
FIG. 1 shows an example of an objective lens drive device which is applied to the prior-art optical pickup device.
As FIG. 1 shows, an objective lens 1 is supported on a bobbin 4, and a focus control drive coil 2 and a tracking control drive coil 3 are attached to the bobbin 4. The bobbin 4 is located between magnets 6, 6 which are provided on a base plate 5 in an opposing relation. The bobbin 4 is supported on the base plate 5 in a cantilever fashion by a pair of supporting rods made of elastic metal and which are extended between front left and right portions of an attaching plate 7 erected on the base plate 5 in parallel to each other.
According to the thus arranged objective lens drive device, when a drive current is supplied to the focus control drive coil 2 or to the tracking control drive coil 3, the bobbin 4 is moved by the elastic displacement of supporting rods 8, whereby an objective lens 11 supported on the bobbin 4 is moved in the focusing direction and in the tracking direction.
In the prior-art objective lens drive device thus constructed, the focusing coil and the tracking coil are mounted on the movable side bobbin which supports thereon the lens system. There is then the substantial disadvantage that the optical characteristic of a lens, especially a plastic lens, will deteriorated because of the heat generated by the coils or that, when the coils are deformed by heat, this will hinder the movement of the bobbin.
Further, the bobbin needs a feeding flexible printed circuit board or the like to be connected to the coils, which unavoidably increases the number of assembly parts. Furthermore, although the movable side bobbin is made as small as possible in order to reduce the weight thereof, the soldering of the flexible printed circuit board to the end of the coil at such small area is very difficult, and the number of assembly processes for connecting the printed circuit board in the base plate side is increased.
In addition, the coils of different shapes are used and many soldering lands are used so that the gravity center of the movable portion cannot be selected with sufficiently high accuracy. Consequently, this requires the inspection and sometimes the repair or replacement of the objective lens drive device. Further, after the assembly-process, the prior-art objective lens drive device is unavoidably affected from a characteristic standpoint.